This invention relates generally to turbine engines, and more specifically, to reducing, if not eliminating, an intense acoustic tone emitted during certain test operating conditions of such engines.
For testing, turbine engines typically are enclosed within a test cell. The test cell is sufficiently large so that the engine is completed enclosed within the cell, and test operators can move about the cell to set test parameters and check engine performance. Under certain operating conditions, and with the engine located within a test cell, an intense acoustic tone is emitted. This tone sometimes is referred to as "cell howl".
The intensity of the tone can sometimes damage the test cell and engine. Known attempts to eliminate cell howl, as described in Jones et al., The Acoustic Response Of Altitude Test Facility Exhaust Systems To Axisymmetric And Two-Dimensional Turbine Engine Exhaust Plumes, DGLR/AIAA 92-02-131, May, 1992, include attempting to optimize a location of the cell exhaust collector relative to an engine nozzle exit, injecting water in an engine exhaust plume, locating volume resonators in the cell exhaust collector, and inserting a secondary concentric duct into the exhaust collector. These known attempts have not proven one hundred percent successful in eliminating cell howl for all engine nozzles, and the howl generated by some nozzles is not even always reduced.